How to open shared inbox in Outlook 2016

We are running Kopano 8.5 and Z-push 2.4.0 on a CentOS 7 server.
We have Outlook 2016 installed on a Windows 2016 RDS with KOE 1.6.282 installed (and visible within Outlook)
We can open a users mailbox, the problem is that we can’t open a shared (non-active) mailbox. In Outlook we can’t find the option to open a shared mailbox. We can open shared mailboxes in the Deskapp.
Can somebody point us in the right direction on how to tackle this problem?